Re: [PATCH v2] clone: Don't segfault on -b specifing a non-commit

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 6, 2019, 01:36 UTC
Message-ID: <xmqqbltpyeel.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20191105043749.GA27601@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

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> I like the logic flow in this function, which is IMHO clearer than the
> existing code. But the "err" thing puzzled me for a moment. I think you
> are trying to tell the difference between the case that both "our" and
> "remote" are NULL, and the case that we saw a non-commit. In either case
> we return NULL, but only one is an error.

Yup.

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> But:
>
>   - I don't think that logic needs to extend down into
>     lookup_commit_reference_gently(); a NULL return from it would always
>     be an error, wouldn't it?

Yes.

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>   - we could probably simplify this by just inlining it into
>     update_head(). Something like:
>
>       if (our)
>               tip = &our->old_oid;
>       else if (remote)
>               tip = &remote->old_oid;
>
>       if (!tip) {
> 	      /*
> 	       * We have no local branch requested with "-b", and the
> 	       * remote HEAD is unborn. There's nothing to update HEAD
> 	       * to, but this state is not an error.
> 	       */
>               return 0;
>       }

I somehow had an impression that Davide was protecting against the case where tip->old_oid is null_oid (cloning from an empty repo?); NULL return from lookup_commit_reference_gently(null_oid) would not deserve a warning from this codepath, and should work just like the way it has worked before these changes.

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>       tip_commit = lookup_commit_reference_gently(...);
>       if (!tip_commit) {
>               /*
>> -	fetch_if_missing = 1;
>> -	err = checkout(submodule_progress);
>> +	if (!err) {
>> +		fetch_if_missing = 1;
>> +		err = checkout(submodule_progress);
>> +	}
>
> This part makes sense. We might want an explanatory comment along the
> lines of:
>
>   /*
>    * Only try to checkout if we successfully updated HEAD; otherwise
>    * HEAD isn't pointing to the thing the user wanted.
>    /
>    if (!err) {
>        ...

Yup.

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>> diff --git a/t/t5609-clone-branch.sh b/t/t5609-clone-branch.sh
>
> I think it would be the case that the remote HEAD is pointing to a
> non-commit (since that's a corrupt repository, it might make sense
> create a separate sub-repository).

All good comments.

Thanks